“In the beginning there was nothing. God said, ‘Let there be light!’ And there was light. There was still nothing, but you could see it a whole lot better.”
Ellen DeGeneres may have been joking when she said this, yet truer words were never spoken. Light helps us to perceive the world around us, but it is so much more. It can enhance beauty, focus our attention and dazzle us. Every good photographer knows that the “golden hour” after sunrise or before sunset has a magical quality unmatched during the rest of the day. A lighthouse, in the gloom of a dark and stormy night, serves as a beacon to ships seeking safe haven. Simple, white light can pass through a crystal to create a wondrous kaleidoscope of color. Yes, light is amazing.
It’s not just about aesthetics, however. Light affects our ability to perform tasks and it impacts our mood and circadian rhythms as well, which is why understanding lighting is so important [Chang, Aeschbach, Duffy, & Czeisler 2015]. But, which light bulb is the right one for each circumstance? It can be very confusing with all the different lamps and light bulbs. Electrical constraints, environmental considerations and various functional requirements compound the issue.
We created this lighting guide to introduce you to many types and shapes of bulbs that are available today and to help you understand the relevant metrics and terminology. We have laid out the requirements of different rooms, tasks and lights. This should help you to make an informed decision when comparing and selecting the right light bulb for your needs.
What types of light bulbs are out there?
Thomas Edison created the first light bulb in 1879. Since then, there has been a myriad of options from which to choose. However, the signing of the Energy Independence and Security Act (EISA) in 2007 legislated stricter standards for lighting in the U.S. It also ushered in a movement toward more eco-friendly, longer lasting and cost-efficient light bulbs. Inefficient and outdated bulbs that cannot meet the new requirements have been or will be phased out.
Light Emitting Diode (LED) bulbs are all the rage today because they create a lot of light, but use very little energy and last a long time. Unlike incandescent and fluorescent light bulbs, LEDs pass electricity between semiconductors, rather than through a filament. Consequently, less heat is generated and more of the energy goes into creating the light. LEDs allocate 95% of the energy toward light production and only 5% is lost as heat. They are also more environmentally friendly than most other bulbs (largely due to this electrical efficiency) and have a lower global warming potential and cumulative energy demand than even CFLs [Principi & Fioretti 2014]. LEDs have a long lifespan (estimated 25,000 hours) because there is less heat and no filament to burn out.
LEDs are usually much more cost-effective than alternative light bulbs, despite a higher individual price tag ($3-$20 for many standard bulbs). You don’t have to continually replace them, so your costs are often less in the long run. Look for the Energy Star certification symbol to ensure that you are purchasing LEDs that have met the rigorous efficiency standards set by EISA.
The incandescent light bulb is the classic design Edison invented. It is comprised of a tungsten filament that glows with light when it’s heated by an electric current within a glass enclosure. Unlike LEDs, an incandescent light bulb expends 95% of the energy it takes in to generate heat and only 5% is converted into light. This makes them very inefficient and increases your electricity bill.
Incandescent light bulbs, however, are relatively inexpensive ($0.50-$5 for most standard bulbs). The downside is that the filament typically burns out within a thousand hours. In the long run, their replacement costs exceed those of LEDs. Many traditional incandescent light bulbs are being discontinued, due to their inability to meet EISA requirements. New technological advances, however, have resulted in higher efficiency incandescent alternatives.
This is the iconic bulb that most people think of when they picture a light bulb. Its low cost and warm yellow-white light, emitted in all directions, makes it a convenient easy choice for many general applications.
These are simply incandescent bulbs that contain halogen gas. As the tungsten burns, the resulting gas is “recycled” back onto the filament with the help of the halogen gas. It produces a brighter and whiter light and is slightly more efficient than traditional incandescent bulbs. It has an expected lifetime that is twice that of general incandescents (roughly 2,000 hours). One drawback of halogen lights is that they tend to “run hot.” They are also a little more expensive than regular incandescent bulbs ($2-$7 for many standard bulbs).
Xenon light bulbs operate in the same way as halogens, but last 10,000 hours. Xenon gas glows when in the presence of an electric current. This enables it to achieve the same brightness while requiring less energy. Unlike halogens, xenon bulbs generate very little heat, while emitting a slightly warmer color light.
Some incandescent bulbs have a reflective coating that focuses their light in one direction. Reflectorized light bulbs put out twice the light of general ones. Parabolic versions control the light with even more precision and emit up to four times the light.
Fluorescent light bulbs create light via a three-step process:
- Electricity ionizes (i.e. removes electrons from) mercury vapor in the bulb
- The released electrons radiate photons at UV wavelengths (i.e. invisible electromagnetic energy)
- This energy is converted into visible light by a phosphor coating on the inside of the bulb
These light bulbs use only 20-33% of the electricity of incandescents and last ten times longer (10,000 hours). They do contain a small amount of mercury, so burnt-out fluorescent bulbs should not simply be thrown out in the trash. Guidelines for proper recycling and disposal can be found on the Environmental Protection Agency website: epa.gov.
CFL (Compact Fluorescent)
These new small fluorescent bulbs often have screw bases that fit most lamp sockets and can be substituted for incandescent bulbs. CFL light bulbs also have many advantages over earlier fluorescents. They turn on right away (no start-up flicker), are quiet and the light is warmer and color-corrected. CFL bulbs are more expensive than most halogen incandescent bulbs but slightly less than LEDs ($2.50-$10 for most standard bulbs).
T8 and T12
These tubular light bulbs are what we typically think of when we hear “fluorescent lights.” They were used almost exclusively for commercial purposes in the past, but technological improvements have made residential applications much more common.
HID (High-Intensity Discharge)
HID bulbs create light by sending an electric current between two tungsten electrodes that are housed in a bulb filled with gas and metallic salts. The gas helps facilitate the generation of an electrical arc, which heats the metal salts and creates a plasma. This amplifies the light produced by the arc. These bulbs are highly efficient and have long lives, but emit a rather unpleasant light, though it has an almost sun-like luminescence. Consequently, they are usually employed in outdoor settings, for security or automotive headlights [Baumann, Schwieger, Wolff, Manders & Suijker 2015].
HIDs can use the following gases/vapors:
- Metal Halide
- High-Pressure Sodium
- Low-Pressure Sodium
- Mercury Vapor
Shapes of light bulbs
Contemporary light bulbs are available in a wide variety of shapes and sizes. This is needed to accommodate the ever-growing number of fixtures, lamps and lighting applications. Each light bulb has its own set of requirements, which can make finding the right one a difficult task.
Understanding labeling codes
Manufacturers have developed a labeling system to help communicate light bulb requirements and recommendations for their lights. If you don’t have a Rosetta Stone for deciphering these codes, however, it can be confusing.
- Bulb – Designations consist of two parts: a letter(s) and a number. The letter represents the shape of the bulb, while the number indicates the width (in eighths of an inch).
- Base – This identifies how the bulb connects to the socket of the light. It is designated by a letter(s) (type) and number (diameter in millimeters).
- Wattage – The electrical power of a light or lamp is expressed in watts.
- Voltage – The force of electricity flow is expressed in volts.
- UL/cUL Approved – The Underwriters Laboratory (U.S. and Canada) inspects, tests and certifies lighting products to ensure safety.
Most common bulb shapes
Below are the most common shapes, their letter designations and typical usage.
- Arbitrary (A) – Standard use for most home lighting
- Bullet or Blunt Tip (B) – Best when used for decorative lights or ceiling fans
- Bulged Reflector (BR) – Interchangeable with Reflector bulbs for recessed track or can lighting
- Bulged or Blown Tube (BT) – Usually used for table lamps
- Conic (C) – Mostly found in small appliances
- Candle (CA) – Great option for decorative use in chandeliers and wall lights
- Circline (CIR) – These can be found in some modern table lamps
- Elliptical (E) – Regular and dimpled versions of this bulb can be found in sports arenas, car dealerships, parking garages and industrial lighting
- Elliptical Reflector (ER) – Most often used in recessed lighting applications in hotels, offices and residences
- Flame (F) – Similar to Candle bulbs, these have blown or etched glass designs that make the light appear to flicker and are used in chandeliers, wall lights and restaurants
- Globe (G) – These spheres are often seen in vanities, marquees or modern chandeliers, pendants and wall lights
- Lantern Chimney (H) – Used in some decorative applications such as chandeliers, post or coach lights
- Mirrored Reflector (MR) – Usually used for commercial or retail accent and spot lighting
- Pear Shaped (PS) – An exaggerated version of the standard A19 type with straight sides, this bulb is used in retail stores and for utility company applications
- Parabolic Aluminized Reflector (PAR) – These hard glass lens bulbs directionally control the light beam from a focused spot to a flood, which makes them great for outdoor use or as recessed downlighting in museums and retail establishments
- Reflector (R) – Interchangeable with Bulged Reflector bulbs for recessed track or can lighting
- Sign (S) – Works with lower wattage lamps or signage in casinos, theaters and hotels
- Spiral or Twist (SPIRAL) – These CFL bulbs can replace the standard household A19s
- Straight Tapered (ST) – An extended version of the Sign bulb that is used in marquees and commercial signage
- Tubular (T) – Based on the type of bulb, these can be used in commercial signage, parking garages or appliances
Base or plug types
The light bulb base or plug type varies from light to light. You need to double check which is required for the socket, before buying a new light bulb. There’s nothing more frustrating than getting home and realizing that you bought the wrong one and having to go back to Home Depot.
Most American home lighting applications use light bulbs with Edison screw bases that simply twist clockwise into the socket. They are designated by the letter E and a number, which represents the diameter in millimeters.
This base typically has two male pins on either side that fit into corresponding female slots in the socket and lock with a clockwise twist. It is the standard in many countries associated with the British Empire and is usually designated by the letters BA, followed by the diameter.
Bi-Pin or Bi-Post (G*)
Two pins or posts extend from the end of these bases and either plug into the socket or twist and lock. The International Electrotechnical Commission (ITC) has designated bi-pin base connectors as the international standard for lamps. They are usually designated by the letter G, followed by either another letter (extra feature) and a number, or just a number that indicates the pin spread in millimeters.
Many small light bulbs utilize a wedge design base. These are similar to Bi-Pin bases, but they have two wires that contact the sides of the socket instead. The wires are typically embedded on the outside of a plastic base that the bulb is mounted on. It’s usually narrower at the tip than at the bulb, which gives it its wedge shape. They are identified by the letter W, followed by other letters which detail the exact type and a number to specify the thickness in millimeters.
What information should you compare when buying a light bulb?
Many lamps and lighting fixtures can accommodate a variety of light bulbs. Your choice can be based on factors that may be ecological, financial, aesthetic or functional. It simply depends on your own individual preference and/or situation. The Federal Trade Commission (FTC) mandates that light bulb manufacturers provide specific information. Look at the Lighting Facts section displayed on packaging for relevant information and to compare light bulb options.
When you look at the light emitted by two bulbs side by side, it’s usually pretty easy to determine which one is brighter. It can be a different story, however, when looking at their labels. If you’re older (and I’ll leave that determination to your own discretion), you grew up thinking that the greater the watts, the brighter the light bulb. Now you have something called a “lumen” to think about.
How do watts and lumens differ?
Before CFLs and LEDs were developed, incandescent bulbs were the most widely used. With this type of light bulb, wattage is a decent reference point to determine comparative brightness. The higher the number of watts, the brighter the bulb burns. But newer lighting technologies make that reference point obsolete.
Wattage is actually a measurement of energy use and not brightness. The more watts, the more energy the bulb consumes to generate light. CFL and LED light bulbs require far less energy than incandescent bulbs to power them. But, they still emit equivalent or brighter light.
A lumen is the appropriate measurement for the amount of light (i.e. brightness) emitted. Bulbs may use the same number of watts, but it is the number of lumens that determines which is brighter. At equivalent wattage, LEDs are much brighter than other light bulb types.
How many lumens do I need?
The shape, size, ceiling height and wall color of your room all affect the brightness required to fill it with ample light. How you use the light is also an important consideration. Do you need it for general ambient light, task lighting or simply accent lighting? Here are rough estimates of the lumens needed by room type and usage.
The estimated annual cost is listed on the labeling of most light bulbs. This is a good way to compare the financial impact of different options if you are putting together an annual budget. One thing to note, however, is that some bulb types last longer than others. You may have to replace them more often, depending on your usage. LED light bulbs are far more expensive than their CFL and incandescent counterparts, but they rarely need to be changed out due to regular wear and tear. This makes them more cost-effective in the long run. Here are estimates of the costs associated with various light bulb types (annual and over 25,000 hours).
Light Bulb Lifetime
How a bulb generates light impacts its expected life. Incandescent bulbs last the shortest amount of time. Their filament expands and contracts as it heats and cools every time electricity passes through it. This leads to metal fatigue until the filament breaks down and the bulb “burns out.” CFL light bulbs don’t have filaments, but their metallic electrodes “evaporate” over time (though longer than incandescents). This results in conductivity failure and creates the familiar blackened ends we recognize in burned-out fluorescent tubes. LED light bulbs excite electrons to create light and have no filament or chemical wear and tear. Consequently, they last an incredibly long time. In fact, they never actually burn out, but simply decrease in luminosity. The estimated lifetime of LED bulbs is calculated to the time they emit 70% of their original brightness – almost always decades-long.
The thermodynamic temperature of light emitted by a bulb determines its appearance and is measured in Kelvins. It has nothing to do with the heat generated by the bulb. Contrary to what we might typically think of regarding color, the higher the temperature, the cooler the light appears. The visual scale for light bulbs runs from warm (candlelight is ~1,900k) to cool (car headlight is ~6,000k). Light color can affect the “feel” of a room or space in the absence of lamp shades or bulb covers. Studies have shown that alertness, mood and cognitive performance are influenced by the color temperature and luminance of light [Li, Wang, Shen, Sun, Xie, Zhang, & Zheng 2017]. So, you might want to be at least aware of the appearance when choosing a light bulb.
Energy Used and Energy Efficiency
If you are more environmentally conscious, you might want to opt for “greener” or more eco-friendly light bulbs that focus on efficiently converting energy into light. Efficiency is determined by dividing the generated light (lumens) by the energy used (watts). LEDs are the most efficient light bulbs, followed by CFLs and then incandescent ones. Bulbs that are more efficient are typically identified by the Energy Star certification seal on the packaging.
What is the right light bulb for different lamps and lights?
Lighting fixtures can have multiple uses but are often selected for a primary function within a room. This use makes a big difference in the type of light bulb you should choose. Lighting manufacturers will list recommended bulb options, but it’s a good idea to have an idea before buying a lamp or fixture.
Table and Floor Lamps
These lamps are typically used as general or task lighting. If you want a dimmable table lamp or floor lamp, a halogen incandescent bulb is a good choice. It produces a nice warm glow in all directions and uses 20-30% less energy than a traditional incandescent bulb. CFL bulbs are great if you don’t need your lamp to dim, provided you can find a suitable color temperature. You should probably look to use a spiral or closed A-shape bulb with warmer light. They tend to be easier on the eyes. You probably don’t need to use LEDs, unless the table lamp is a heavily-used desk light. LED light bulbs are often one-directional and considerably more expensive.
Recessed and Flush Mount Ceiling Lights
These high-use lights can be used for ambient, task or accent lighting. However, given the continual use and relative inaccessibility (which makes changing them out a bit more troublesome), they are best served by LEDs. These eco-friendly light bulbs use 80% less energy than equivalent incandescent replacements. They also have much longer lives than fluorescent light bulbs and are significantly brighter than both replacement types. Recessed or flush mount ceiling lights usually have a diffuser that minimizes harsh light that can be caused by exposed LEDs. For recessed or track indoor lighting, reflector or bulged reflector bulbs are great options. Many flush mount lights also work well with standard A type or spiral-shaped bulbs.
These hanging fixtures are typically used for general or task lighting in kitchens above countertops or in dining rooms above tables. They may be occasionally employed in specialized work areas in the home or in more industrial workplaces when there are extremely high ceilings. You’ll likely want to avoid many LEDs in favor of a traditional A-shape or globe-shaped CFL or halogen incandescent light bulb. A portion of the bulb is often exposed, so you should be mindful. Looking directly at certain LED light bulbs isn’t quite as bad as staring at the sun, but it’s not pleasant and could disrupt your ability to complete a task.
These dramatic hanging light fixtures are as much about form as function. Consequently, chandelier light bulbs are often more stylish in their design, especially if they are exposed. These lights are usually used for general or ambient lighting in dining rooms, entryways and bedrooms. Although, many large family rooms or high ceiling common areas often incorporate grand chandeliers to help fill the space or make it feel cozier. Candle, flame or globe-shaped bulbs work well in chandeliers and are typically incandescent. However, newer LED options have been developed that might also do the trick.
Wall Lights and Sconces
These wall mounted lighting fixtures tend to be used for more ambient purposes. Certain areas of the home and office need some light in order to serve their purpose, but bright task lighting is often overkill. A little subdued mood lighting is sometimes helpful to transition from busy common areas to more intimate ones. Many wall lights are small and have confined lamping fixtures. In those cases, use smaller candle or flame-shaped CFLs or incandescent bulbs. Their decorative styling is also aesthetically pleasing and is reminiscent of traditional, pre-electricity lighting. If your interior design is more contemporary, small globe bulbs work well.
Lighting the exterior of your house is also important. Walkways and entries need to be well-lit so that people can safely find their way. Similarly, decks and patios need light for entertaining at night but don’t necessarily need as much illumination. Regardless of the outdoor location, these general or task lights must be durable to withstand the elements. Halogen incandescent light bulbs are usually sufficient for outdoor lighting unless they are continually in use or need to be extremely bright. CFLs do not turn on well or last as long in cold weather, so your geographical location has to be considered. LED light bulbs are great for lighting basketball or tennis courts, but the higher cost may be harder to justify for other uses. Reflector or parabolic aluminized reflector (PAR) bulbs are great for many recessed or spot outdoor applications.
Recent Trend – Vintage Style Edison Bulbs
The growing popularity of rustic, steampunk and industrial interior design and lighting has spurred interest in Edison filament style light bulbs. Originally, these vintage light bulbs were incandescent and had wound filaments that were visible through clear glass casings. Recent LED technology, however, has opened up the possibilities with new internal “filament” configurations and bulb shapes. Now, Edison light bulbs can be used in virtually any lamp or light fixture. Their warm, glowing orange light is probably more aesthetic than functional, but they do look really cool.
Shedding some light on the subject
As you can see, there are a lot of factors that you can evaluate when choosing a light bulb. The use and room help to determine the best lighting fixture, which in turn has technical requirements and size constraints. Even after sorting through those decisions, you still have your own subjective style, economic and environmental considerations to answer to. This guide should give you a head start and help you better understand your choices.
With all the time, energy and money you spend on furniture and home decor, it’s only right that you see it a whole lot better with the right light. Ellen Degeneres was right, but then again, she’s always been one of the brighter bulbs in the box.
How do you dispose of light bulbs?
At some point, regardless of how good a light bulb is, it burns out or gets broken. But what do you do with old light bulbs? Based on the type of bulb and where you live, there are essentially two options: recycle them or throw them out. Each type of light bulb has its own requirements or recommended steps. Take a look at our FAQs for answers.
Frequently Asked Questions – Lighting
These types of light bulbs contain mercury, which is a toxic substance, so many places have laws that prohibit disposing of them in the trash. Check with your local recycling center or garbage service to see if it’s okay to throw CFLs and other fluorescent bulbs in the trash. The following states have made it illegal to throw them out: CA, ME, MA, MN, NH, VT and WA. If it’s legal to throw them out in your area, be sure to wrap fluorescent or CFL bulbs in a paper bag. Even if it’s legal to dispose of them in the garbage, try to recycle them if at all possible – every little bit of eco-friendly behavior helps.
Incandescent bulbs don’t contain hazardous toxic materials, so it’s okay to simply throw them in the trash. Because they’re typically made of thin and fragile glass, it’s generally a good idea to wrap them in a paper grocery bag or heavy plastic bag to minimize the chance of shattering or at least prevent glass shards from scattering.
Halogen bulbs are also toxin-free, so it’s safe to toss them in the garbage too. Most halogen light bulbs are more durable than their incandescent counterparts, so it’s not always necessary to wrap them in protective materials before throwing them away.
These energy efficient bulbs do not contain mercury, so you can throw them in the trash. However, LED light bulbs contain many recyclable materials, so it’s a good idea to recycle them if you can. Recycling centers may handle LEDs differently than fluorescent and CFL light bulbs, so be sure to keep them separated when you make your drop off.
The EPA recommends that you visit Earth 911 to identify local recycling centers that accept light bulbs and other recyclable items and materials. In addition to formal receiving centers, some large retailers like Home Depot or IKEA offer drop-off bins for light bulbs purchased through them.
Other lighting resources
- American National Standards Institute (ANSI) – Establishes a voluntary standardization system for the U.S. private sector
- Department of Energy (DOE) – Addresses U.S. energy and environmental challenges via scientific and technological solutions
- Consumer Reports – Empowers consumers with product knowledge they can trust to make better purchase decisions
- Baumann, B., Schwieger, J., Wolff, M., Manders, F., & Suijker, J. (2015). Numerical investigation of symmetry breaking and critical behavior of the acoustic streaming field in high-intensity discharge lamps. Journal of Physics D: Applied Physics, 48(25), 255501.
- Chang, A. M., Aeschbach, D., Duffy, J. F., & Czeisler, C. A. (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. Proceedings of the National Academy of Sciences, 112(4), 1232-1237.
- Li, H., Wang, H., Shen, J., Sun, P., Xie, T., Zhang, S., & Zheng, Z. (2017, September). Non-visual biological effects of light on human cognition, alertness, and mood. In Light in Nature VI (Vol. 10367, p. 103670D). International Society for Optics and Photonics.
- Principi, P., & Fioretti, R. (2014). A comparative life cycle assessment of luminaires for general lighting for the office–compact fluorescent (CFL) vs Light Emitting Diode (LED)–a case study. Journal of Cleaner Production, 83, 96-107.